Voltage Agnostic Power Reactor

ABSTRACT

Distributed series reactance modules and active impedance injection modules that are adapted to operating with electric power transmission lines over a wide range of transmission voltages are disclosed. Key elements include a virtual ground, an enclosure that acts as a Faraday shield, radio frequency or microwave control methods and the use of corona rings.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 15/055,422 filed Feb. 26, 2016, which claims the benefit ofU.S. Provisional Patent Application No. 62/264,739 filed Dec. 8, 2015,the disclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to systems and methods for dynamic linebalancing of high-voltage (HV) transmission lines using spatiallydistributed active impedance injection modules that are connecteddirectly in series with the HV transmission lines that form the HVelectric power grid.

2. Prior Art

HV electric power grids typically operate at voltages that are on theorder of about 50 kV up to about 600 kV, with the expectation of evenhigher voltages in the future. One of the requirements of these HV powergrids is the need for dynamic distributed active power-flow controlcapability that can inject both inductive and capacitive impedance on tothe HV transmission line as required to achieve line balancing and phaseangle correction. A system that can react fast to the problems of powerflow over the grid will greatly improve the grid operation andpower-transfer efficiency.

Congested networks limit system reliability and increase the cost ofpower delivery by having part of the power dissipated in unbalancedcircuits causing loop currents with associated power loss. In addition,substantially out-of-phase voltages and currents on the transmissionlines reduce the capacity of the lines to transfer real power from thegenerator to the distribution substation. To remove this limitation, itis desired to have HV power grids with transmission lines that arebalanced, with power transfer shared substantially per optimizationmethods, with reasonable power factor, and controllable phase differencebetween voltage and currents. These improvements reduce the loopcurrents and associated losses and enable real power transfer over thegrid up to the capacity of the lines.

Most of the grid control capabilities today are ground based andinstalled at substations with switchable inductive and capacitive loads.These installations require high-voltage insulation and high-currentswitching capabilities. Being at the substations these can use methodsof cooling that include oil cooling, forced recirculation of coolant,and other options without consideration of the weight and size of theunits. These lumped controls require a centralized data collection andcontrol facility to coordinate operation across the grid and hence haveassociated delays in implementing the control function on the powergrid.

Distributed and active control of transmission line impedance, ifeffectively implemented with high reliability, improves the systemefficiency substantially, but requires cost-effective implementationsthat can alter the impedance of the HV transmission lines, with fastidentification and fast response to line-balance issues, by changing thephase angle of the current-voltage relationship applied across the line,thus controlling power flow.

At present proven effective and reliable solutions for distributedcontrol of the power grid as, for example, described in U.S. Pat. No.7,835,128 to Divan et al (the '128 patent) are limited. FIG. 1 shows arepresentation of the present-day distributed line balancing system 102using a “distributed series reactor (DSR)” 100 using a passiveimpedance-injection module.

The patents U.S. Pat. No. 8,816,527, “Phase balancing of powertransmission system,” and U.S. Pat. No. 9,172.246, “Phase balancing ofpower transmission system,” by Ramsay et al. also refer to systemsutilizing a single turn primary winding without requiring a break in thepower line. Those patents also disclose using a housing preferablyconfigured to reduce the potential for Corona discharges.

Power is transmitted from the electric power source or generator 104 tothe load or distribution substation 106. Spatially distributed passiveinductive impedance injection modules or DSR 100 are directly attachedto the power conductor on the HV transmission line 108, and hence formthe primary winding of the DSR 100 with a secondary winding having abypass switch that, when open, inject an inductive impedance on to theline for distributed control. These DSR 100s only provide a limitedamount of control by injecting only the inductive impedance on to theline. When the secondary winding is shorted by the bypass switch, theDSR 100 is in a protection mode and injects substantially zero impedanceon to the HV line.

FIGS. 2 and 2A and 2B show embodiments of a passive impedance injectionmodule DSR 100. The HV transmission line 108 is incorporated into themodule as the primary winding by adding two split-core sections 132 thatare assembled around the HV transmission line 108. The core sections 132are attached to the HV transmission line 108 with an air gap 138separating the sections after assembly. The air gap 138 is used to set amaximum value of fixed inductive impedance that is to be injected on theHV line via the primary winding. Secondary winding 134 and 136 encirclesthe two split-core sections 132 and enables the bypass switch 122 toshort out the secondary winding and prevents injection of inductiveimpedance on to the a HV transmission line 108 and also providesprotection to the secondary circuits when power surges occur on the HVtransmission line. The split core sections 132 and the windings 134 and136 comprise the single-turn transformer (STT) 120. A power supplymodule 128 derives power from the secondary windings 134 and 136 of theSTT 120 either via the series-connected current transformer winding 126or via the alternate parallel-connected winding. The power supply 128provides power to a controller 130. The controller 130 monitors the linecurrent via the secondary current of the STT 120, and turns the bypassswitch 122 off when the line current reaches and exceeds a predeterminedlevel. With the contact switch 122 open, a thyristor 124 may be used tocontrol the injected inductive impedance to a value up to the maximumset by the air gap 138 of DSR 100.

When using multiple DSRs 100 connected on the HV transmission line as inFIG. 1, the inductive impedance injected by all the DSRs 100 on the linesegments provides the total control impedance. The main reason for thechoice and use of inductive impedance injection unit DSR 100 is itssimplicity, inexpensiveness, and reliability, as it does not need activeelectronic circuits to generate the needed inductive impedance. Thevalue of the inductive impedance of each DSR 100 is provided by theair-gap setting of the transformer core and not electronicallygenerated, and hence has fewer failure modes than if the same wasimplemented using electronic circuits. The difficulty in implementingand using electronic circuits for impedance injection units that canproduce actively controllable high impedance for injection comprisingboth inductive and capacitive impedance is multi fold. It includesachieving, the long-term reliability demanded by electric utilitieswhile generating the voltage and current levels, that are needed toachieve effective active control of the lines in the secondary circuit,while remaining within reasonable cost limits for the module.

Distributed active impedance injection modules on high-voltagetransmission lines have been proposed in the past. U.S. Pat. No.7,105,952 of Divan et al. licensed to the applicant entity is an exampleof such. FIG. 3 shows an exemplary schematic of an active distributedimpedance injection module 300. These modules 300 are expected to beinstalled in the same location on the HV power line as the passiveimpedance injection modules (or “DSR” 100) shown FIG. 1. The activeimpedance injection module 300 does not perform the same functions. Infact the active impedance injection module 300 does not have a gappedcore 132 of FIG. 2B that provides the fixed inductive impedance. Insteadthe inductive or capacitive impedance is generated using the converter305 based on the sensed HV transmission line 108 current. Sampling thesecondary current by the series-connected secondary transformer 302 doesthe sensing of the magnitude of the line current. The sensing and powersupply block 303 connected to the secondary transformer 302 extracts theHV transmission-line current information and feeds the controller 306.The controller based on the received input provides the necessarycommands to the converter 305 to generate the required inductive orcapacitive impedance to adjust the line impedance. The value of theimpedance in this case is not fixed but can be made to vary according tothe status of the measured current on the HV transmission line. Hencethe system using spatially distributed active impedance injectionmodules 300 provides for a much smoother and efficient method forbalancing the grid.

In practice the active impedance injection modules 300 have not beenpractical due to reasons of cost and reliability. In order to inject theneeded impedances on to the HV transmission line for providingreasonable line balancing there is a need to generate a significantamount of power in the converter circuits. This has required the activeimpedance injection modules 300 to use specialized devices with adequatevoltages and currents ratings.

The failure of a module in a spatially distributed inductive-impedanceinjection-line balancing system using DSR 100 modules inserts anear-zero impedance (equal to the leakage impedance) set by the shortedsecondary winding or substantially zero impedance on to the line.Failure of a few modules out of a large number distributed over the HVtransmission line does not mandate the immediate shutdown of the line.The repairs or replacement of the failed modules can be undertaken at atime when the line can be brought down with minimum impact on the powerflow on the grid. On the other hand, for utilities to implementdistributed active line balancing, the individual modules must beextremely reliable. These also have to be cost effective to be acceptedby the Utilities.

Power transmission line balancing circuits have been limited to the useof delayed-acting heavy-duty fully-insulated oil-cooled inductive andcapacitive impedance injectors or phase-shifting transformers prone tosingle-point failures, located at substations where repairs of thesefailed units can be handled without major impact on power transfer overthe grid.

As described above the use the specialized devices that can handle theneeded power with high reliability demanded by the utilities at areasonable cost has not been possible so far. There is a need for such acapability for converting the grid to a more efficient and intelligentsystem for power distribution. If it can be established, it will have amajor impact on the efficiency and capabilities of the grid. Sinceelectric power distribution systems vary in their operating voltagelevels, the availability of modules that tolerate a wide range ofoperating voltages, will offer a grid operator further economies inprocurement and inventory management.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings are meant only to help distinguish the invention from theprior art. The objects, features and advantages of the invention aredetailed in the description taken together with the drawings.

FIG. 1 is a representation of a high voltage transmission line showingdistributed passive impedance injection modules attached directly to theHV transmission line. (Prior art)

FIG. 2 is an exemplary block diagram 200 of an inductive impedanceinjection module using a single turn transformer for distributedinductive impedance injection on a HV transmission line. (Prior art)

FIGS. 2A and 2B are exemplary schematics of the single turn transformerused in the passive impedance injection module of FIG. 2. (Prior Art)

FIG. 3 is an exemplary block diagram 300 of an active impedanceinjection module, licensed to the current entity, using a single-turntransformer for distributed active impedance injection on to a HVtransmission line. (Prior Art)

FIG. 4 is an exemplary block diagram 400 of an embodiment of thedisclosed active impedance injection module using multi-turn primarywindings for distributed active impedance injection on a HV transmissionline.

FIG. 4A is an exemplary schematic of the multi-turn primary transformeras per an embodiment of the current invention. The multiple secondaryturns are deliberately not shown in order to provide a simpler drawing.

FIG. 4B shows an exemplary cross section of the multi-turn transformerof FIG. 4A.

FIG. 5 is a representation of a high voltage transmission line showingvarious ways the distributed active impedance injection modules are tobe supported while being directly attached to the HV-transmission linesand operating at line voltage as per the embodiments of the invention.

FIG. 6 is a block diagram of a DSR module having features that assistits adaptation to a variety of operating voltage environments.

FIG. 7 is a block diagram of a simpler, multiturn DSR module havingfeatures that assist its adaptation to a variety of operating voltages.

FIG. 8 is representation of a DSR module having an arbitrary shapeemploying corona rings that assist its adaptation to a variety ofoperating voltage environments by avoiding electrical discharge.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As discussed above there is a need to have high-reliability,fault-tolerant and intelligent distributed dynamic-control modules(distributed active impedance injection modules) with capability toinject both inductance and capacitive impedances of sufficient andappropriate magnitude on to high-voltage transmission lines to enabledistributed power flow control. These distributed dynamic controlmodules are directly attached to the HV-Transmission line and are atline potential while in operation. The distributed dynamic controlmodules are enabled to operate by extracting power from theHV-Transmission line for control and for generating the necessaryvoltages to be impressed on the High Voltage (HV) transmission line. Themodules generate voltages at the right phase angle for injection on tothe HV-transmission line, through the multi-turn transformer, to providethe necessary inductive or capacitive impedance during operation.

The invention disclosed the use of the multi-turn transformer havingmulti-turn primary winding connected in series with the HV transmissionline 108 by cutting and splicing in the winding. The secondary side ofthe multi-turn transformer and all associated circuitry are electricallyisolated from the ground. However, one side of the secondary winding isconnected to the primary winding to provide a virtual ground or“floating ground” reference and also partly to protect thesecondary-side circuits form stray fields. Alternately the virtualground 408 can be established by connecting the negative dc link of theinverter/electronic injection module to the HV transmission line.Further, both may be grounded for effective operation. Differentpower-electronics topologies may necessitate other grounding schemes andthese schemes do not affect the key invention but, rather, are specificimplementations.

In order for the distributed control modules to be successfully acceptedby utilities and installed on lines, these distributed control moduleshave to be smart and self-aware, remotely controllable and configurable.The modules should be of a reasonable weight compared to the linesegment over which these are to be installed, even where the modules aresuspended in an insulated fashion from the towers or are supported byadditional support structures. These should also have a low windresistance to reduce the effect of wind loading on theline/tower/special support structure employed. As an essential featureall the electronic components and circuits of the module should havevery high reliability to reduce the probability of line down times dueto failure of the modules/components used therein. The splicingconnection of the module to the HV transmission line also has to havehigh reliability.

The invention disclosed provides distributed active control having veryhigh reliability and capability for power flow and line balancing acrossthe multiple high-voltage transmission lines used for power transmissionon the high power grid system. The invention overcomes the issues of theprior art implementations discussed and meet the criteria set for theuse of the distributed control modules that are discussed below.

There are multiple requirements that have been defined for achieving theuse of distributed control that need changes from the prior artimplementations. These are:

-   -   1. The need is to have a distributed module that can generate        and supply the required range of inductive and capacitive        impedances (generating the necessary leading or lagging power)        to the transmission line to provide the necessary control for        line balancing.    -   2. Provide the above capability at a reasonable cost        point—preferably by using standard off-the-shelf        power-electronics components; this means that the secondary        winding and associated circuits operate at voltages and current        levels normally seen in high-volume power-electronic        applications. Using off-the-shelf power-electronics components        means using general-purpose power-electronics components that        are also manufactured and sold in the ordinary course of        business for other uses.    -   3. The third is the need for reliability of the distributed        modules to be high enough to eliminate failures and related line        shut downs to an acceptable level for the Utilities—this is        achievable if standard power-electronics components, with        associated high reliability can be used in the secondary        circuits.    -   4. The final need is to have relatively low weight and low        wind-capture cross section for the module to be attached to the        HV-transmission line directly or with minimum extra support.

The disclosed invention provides for improvement in all the aboveaspects in the embodiments disclosed below:

The prior art dynamic injection modules had problems, which preventedtheir acceptance. One was the need for specialized components for thegeneration of the magnitude of injection power (voltage and current) tobe generated to provide adequate control of the HV transmission linesegment where the module is attached. The second was the lack ofreliability due to the modules handling high power levels, which againnecessitated specially tested and qualified component use. Both theabove requirements resulted in the cost of the module also being veryhigh for use by utilities.

The disclosed invention for increasing the impressed voltage orimpedance on the transmission line uses multiple turns on the primarywinding of a series-connected injection transformer. Increasing thenumber of turns in the primary winding alters the turns ratio of thetransformer, and allows the distributed active impedance injectionmodule (injection module) to have a greater impact. Since the primarywinding of the injection transformer needs to be in series with the HVtransmission line, the use of additional turns of the primary windingrequires the HV transmission line to be cut and the ends of the windingto be spliced in series with the HV transmission line. Further havingmultiple turns of heavy-duty wire, capable of carrying the line currentsseen on the power grid and the use of a heavier core to provide therequired coupling/flux linkage to the line, increases the weight andwind-capture cross section of the injection module. Though the injectionmodules are still attachable directly to the line, it is preferable toprovide additional support for the heavier injection modules of thepresent invention due to its additional weight.

The advantages of the disclosed multi-turn primary transformer includethe ability to inject higher voltages, with 90-degree lead or lag angle,providing inductive or capacitive impedances respectively, on to the HVtransmission line for power flow control and grid optimization. Withmore turns, the transformer can also be designed such that thepower-rating-to-weight ratio (kVA per kg) of the unit can be increased,increasing the economy of the unit as well. The use of the multi-turnprimary winding also allows the preferred use of non-gapped transformercore, with high-permeability core materials, thereby reducing the fluxleakage and improving power transfer between the primary and secondarywindings. This, and the careful selection of the number of secondaryturns as a ratio of the primary turns, further reduces the dynamicsecondary voltages that have to be generated for the required injectionof voltages with the correct phase for line balancing. The lower voltagerequired to be generated across the secondary winding, to achieve thehigh kVA injection, due to the carefully selected ratio of the primaryto secondary windings, enable high-volume power semiconductors andcomponents to be used. The use of these semiconductors and components inthe secondary circuit of the transformer (for the control module, thepower converter generating the necessary leading or lagging voltages andprotection circuits including the shorting switch) make the module verycost-effective. Further the use of lower voltages in the secondarycircuits with associated power electronic components with sufficientvoltage margins provide the necessary reliability of operation for thesecircuits connected across the secondary windings to satisfy thereliability requirements of the utilities for use of the distributedmodules.

Further using the distributed approach, with the impedance injectionmodules, allows for significantly greater “N+X” system reliability,where N is the required number of distributed modules, and X is thenumber of extra redundant modules. Therefore, by ensuring thereliability of each unit by itself being sufficient for use by theutilities, the added extra redundant distributed active-impedancecontrol modules provide an additional layer of “system” reliability overand above the unit reliability. The use of these distributed impedanceinjection modules also provides the intelligence at the point of impact,for providing fast response to any changes in the optimumcharacteristics of the lines while transferring power. This in turnresults in a grid using distributed injection modules of highreliability, capable of providing very high system reliability,acceptable to all the utilities. The use of the distributed impedanceinjection modules hence are enabled to provide the best capability tobalance the power transmitted over the HV-transmission-lines of thepower grid.

FIG. 4 is an exemplary block diagram 400 of an implementation of theactive impedance injection module (injection module) of the currentinvention. The injection module 400 comprises a multi-turn transformer400A that has its primary winding 403 connected directly to thetransmission line 108 by breaking the line and attaching the two ends ofthe primary winding 403, by splicing into the line segment as shown inFIG. 4A at 401 and 402. The primary winding 403, is in series with theHV transmission line, 108 and carries the total current carried by thetransmission line, 108. In order to reduce losses due to skin effect inthe conductors and thereby reduce the heating of the conductors used inthe primary winding, 403 of the multi-turn transformer 400A, a ribbonconductor or continuously transported cable or a braided ribbonconductor may be used, instead of the standard conductor, for theprimary winding 403, as shown in the exemplary cross section FIG. 4B ofthe multi-turn transformer, 400A. The ribbon/braided ribbon conductorwhen used, also helps to reduce the over all weight of the conductorused and hence reduce the weight of the whole injection module 400. Aconductive foil may also be used instead of the standard conductor insome cases to reduce the weight and improve the current carryingcapability. A non-gapped transformer core 409, of high permittivitymaterial, is used to allow the maximum coupling possible between theprimary winding 403 and the secondary winding 404 of the multi-turntransformer 400A. In this instance it is essential to have the splicingsystem design to be made robust to withstand the stresses that thesplicing system will be subject to in the event of a utility-level faultcurrent and to the normal thermal cycles during daily operation, tominimize the chance that splicing unit 401 and 402 failure will takedown the line 108. The secondary winding 404 of the transformer couplesto the primary winding 403 and is floating with respect to the primarywinding. An exemplary virtual ground at the potential of the HVtransmission line 108 is established by connecting one side of thesecondary winding of the multi-turn transformer to the HV transmissionline that enables the injection module 400 itself to be floating at highvoltage of the HV transmission line 108 during operation.

A second low-voltage transformer 302 in the secondary circuit isconnected to a power supply 303 within the injector module 400 thatgenerates the necessary power required for the low-voltage electronicscomprising the sensing, communication and control circuitry, all ofwhich are lumped in the block diagram of the module as controller 406,the voltage converter 405 and the secondary winding shorting switch 304.The voltage converter or simply converter 405 may be of any appropriatedesign, as such devices of various designs are well known in the art.Typically, such devices are configured to inject an inductive load ontothe high voltage transmission line and may also have the capability ofinjecting a capacitive load on the transmission for power factor controland may further be capable of controlling harmonic content in thehigh-voltage transmission line. Such devices are also known by othernames, such as by way of example, inverters or converters/inverters. Anexemplary device of this general type is the combination of the inverter71 and energy storage 74 of U.S. Pat. No. 7,105,952, though many otherexamples of such devices are well known. These devices typically act asactive impedances to controllably impose the desired impedance onto thehigh-voltage transmission line. Also preferably the controller 410 usedin the preferred embodiments includes a transceiver for receivingcontrol signals and reporting on high voltage transmission lineconditions, etc.

The shorting switch 304 is activated to prevent damage to the circuitsconnected across the secondary winding 404 during occurrence of hightransients on the HV transmission line due to a short circuit orlightning strikes, or even for prolonged overloads The controller 406has sensor circuitry for monitoring the status of the line and fortriggering the protection circuits 304, and a transceiver establishing acommunication capability 410 for inter-link communication and foraccepting external configuration and control commands, which are used toprovide additional instructions to the converter 406. The voltageconverter 405 is an active voltage converter that, based on input fromthe controller 406, generates the necessary leading or lagging voltagesof sufficient magnitude, to be impressed on the secondary winding 404 ofthe power line transformer of the distributed active impedance injectionmodule 400, to be coupled to the HV transmission line 108 through theseries-connected multi-turn primary winding 403 of the transformer. Thisinjected voltage at the appropriate phase angle is able to provide thenecessary impedance input capability for balancing the power transferover the grid in a distributed fashion. The multi-turn primary 403 ofthe disclosed transformer 400A coupled to the HV-transmission line 108is hence the main enabler for implementing the active distributedcontrol of the power transfer and balancing of the grid.

The current application addresses the advantages and features of the useof multi-turn secondary windings 403 of a distributed active impedanceinjection module (injector module) 400 attached to the HV transmissionline 108. By using a multi-turn primary winding 403 the multi-turntransformer 400A is able to impress a higher voltage on the power HVtransmission line with a given transformer core size and weight whilethe connected circuits of the secondary winding 404 (converter 405,controller 406 and protection switch 304) of the transformer 400A areable to operate at lower voltage ranges with the proper turns ratioselection, that are typical of power-electronics components commerciallyavailable. This enables a cost-effective product using standardcomponents and devices while providing the needed high reliability tothe modules and high reliability to the grid system. The use of thistype of injection module 400 allows fast response to changes in loadingof the HV transmission lines at or close to the point of change fordynamic control and balancing of the transmission lines. By providingthe capability for injection of sufficiently large inductive andcapacitive loads in line segments using reliable distributed injectormodules 400, the over all system stability is also improved. Theinjector module 400 of the current invention is not confined tosubstations, as in the past, but is enabled to provide power flowcontrol capability within existing utility right-of-way corridors in adistributed fashion. The use of multi-turn primary winding 403 alsoallows the typical use of non-gapped core for the transformer improvingthe weight and power transfer coupling of the device to the HVtransmission line 108.

It should be understood that all the associated circuits of the moduleare enclosed in a housing, which is suspended insulated from ground atthe HV transmission line voltage. Due to weight considerations it ispreferable to have these modules suspended from the towers or provideadditional support for their safe attachment. FIG. 5 shows the typicalattachment methods 500 possible for supporting the injection modules 400connected to the HV transmission lines 108. The on-line attachment 501,is the typical prior art attachment used for the static modules, whichconnects the module to the line directly, with no additional support andlets the line supports take the weight of the module and the line.Though this is acceptable, this type of attachment is not the preferredone for the injection modules 400, of the current invention. Thepreferred attachment for these impedance injection modules 400,distributed for line balancing over the grid system, are with additionalsupport, directly connected by supporting insulators 502 on the HVtransmission towers 510 or by using special support structures 511 withinsulated supports 503 for providing the additional weight carryingcapability for the distributed module. The above support methods alsoimprove the reliability of the structures and system during extremeclimatic disturbances.

The fact that both active impedance injection (AII) and distributedseries reactor (DSR) modules are to be suspended in contact with highvoltage transmission lines, measures must be taken to insure theirreliable operation in that environment. The first measure, asillustrated in FIG. 4, is to provide a local floating ground connection408. FIG. 6 shows a passive DSR similar to that in FIG. 2, but it adds aconductive housing 618 which acts as a Faraday shield for the operatingcomponents internal to the DSR module, minimizing their disturbance byelectrical events external to the DSR. This housing is connected to thelocal floating ground 608. A similar conductive housing is used with anAII module. While each of FIG. 4 and FIG. 6 show the virtual groundconnection directly to the powerline 108, the virtual ground connectioncan be made to an electrically equivalent point within the module, forinstance to the terminal 402 in FIG. 4 or terminal 702 in FIG. 7. Thevirtual ground is a single connection to the powerline or to anelectrically equivalent point.

Other elements of FIG. 6 are the power transmission line 108, which actsas a single turn primary for the principal reactance transformer thatalso includes a ferromagnetic core 602 and a secondary winding 604. Thesecondary winding 604 is bridged by a contactor 610 and bybi-directional thyristors 620. The contactor 610 is principally usefulto reduce the reactance injected into the transmission line toessentially zero when it is closed, but it also lends importantprotection under fault conditions. The thyristor pair 620 may beconfigured to respond to the controller 612 and modulate the reactanceinjected into the power transmission line 108, they may be configured toact as an overvoltage protection circuit under fault conditions, or theymay be configured to serve both roles, as detailed by U.S. Pat. No.9,172.246 (Ramsay, et al., “Phase balancing of transmission system”).Element 612 is a controller, that responds to internal demands, forinstance from the powerline monitor 614, or it may respond to messagesreceived by the radio transceiver 630, which receives signals 640 from acentral power management system. The transceiver 630 is also optionallycapable of reporting the output of the powerline monitor 614 to thecentral power management system.

In the embodiment of FIG. 6, the powerline monitoring and system powersupply 616 are both coupled to the transmission line 108 by a secondferromagnetic core 603 and an associated secondary winding 605. As shownin FIG. 3 and FIG. 4, the local system power and powerline monitoringmay be accomplished by connecting the appropriate circuits 303 to thesecondary winding 604 of the principal reactance transformer.Alternatively, as described above, the principal reactance transformermay have multiple secondary windings, serving to support injectedreactance, powerline monitoring and local system power.

The distributed series reactor systems cited here have to operate at thepowerline voltages ranging from 50,000 volts to 600,000 volts, andeventually to the vicinity of one megavolt. Consequently, conductiveelectrical connections for control purposes are out of the question,unless they use the high voltage lines as a data transmission medium.This invention depends upon the use of microwave or other radiofrequency signals 640 for communications to and from a central controlsystem. Such communications may use any one of the Industrial,Scientific, and Medical (ISM) radio bands for local communicationbetween the DSR and a terminal at ground potential. Depending upon theoverall system architecture, long haul communications may be effected bythe public cellular network, private wired networks or microwavenetworks. FIG. 4 shows a similar microwave or radio frequency connectionfor an AII module.

While FIG. 6 shows the powerline 108 serving as a single-turn primary,all the features of that figure are equally applicable if the primaryhas multiple turns, as illustrated in FIG. 4, element 403. A distributedseries reactor DSR can be constructed with a multiple turn primary likethat illustrated for the active impedance injector in FIG. 4.

While the reactance injection units of FIG. 4 and FIG. 6 incorporateelectronic control modules, inductive reactance can be inserted into apowerline with a much simpler system. However, since this reactance mustbe in series with the power transmission line, it must also toleratehigh voltages, ranging from 50,000 volts to 600,000 volts, and possiblybeyond into higher voltages. A simple inductive reactance module isillustrated in the block diagram of FIG. 7. This module attaches inseries with the power transmission line 108, and it consists mainly of aprimary winding 703 coupled to a ferromagnetic core 709. As a practicalmatter, connection to the power transmission line 108 is done by usingconductive mechanical contacts 701 and 702. The voltage tolerance isassured by providing a virtual ground to the conductive enclosure 718using a direct contact 708 to one end of the reactor 703, effectivelytying the case to the potential of the power transmission line 108.

It will be appreciated that a reactor of FIG. 7 will be used withexternal circuitry to provide control, typically by the use of ashorting relay, and protection typically by the use of paralleledsilicon controlled rectifiers. Such control and protection might beplaced in parallel with a single reactance module like FIG. 7, or thecontrol and protection could be placed in parallel with two or morereactance modules like FIG. 7, connected in series.

Ideally, no external part of a distributed series reactor would have aradius of curvature sufficiently small to allow corona discharge at highoperating voltages. As a practical matter, particularly as higherpowerline voltages are used, that is not a reasonable expectation. FIG.8 shows a DSR module having an arbitrary shape. In FIG. 8, element 860is a conductive case, connected to the local virtual ground (608 in FIG.6 and 708 in FIG. 7). In FIG. 8, one of two powerline connections 800 isshown, and it has a twin on the hidden side; the two duplicate thefunction of elements 401 and 402 in FIG. 4. FIG. 8 also shows amechanical support 870 and an exposed portion of a principal reactortransformer core 880. In the case of a fixed reactor as shown in FIG. 7,880 is the ferromagnetic core of that reactor. In order to support highoperating voltages, two corona rings 820 and 822 are affixed to the case860. The radii of curvature of the corona rings are all large enough toavoid electrical discharge, and they provide an electrostatic shieldingfunction for the components inside them. While two corona rings havebeen shown, more may be used. In some cases, it may be desirable to havecascaded corona rings, smaller ones near the DSR case 860 and largerones located at a larger distance from the case and its support 870.

Even though the invention disclosed is described using specificimplementation, it is intended only to be exemplary and non-limiting.The practitioners of the art will be able to understand and modify thesame based on new innovations and concepts, as they are made available.The invention is intended to encompass these modifications.

Thus the present invention has a number of aspects, which aspects may bepracticed alone or in various combinations or sub-combinations, asdesired. Also while certain preferred embodiments of the presentinvention have been disclosed and described herein for purposes ofexemplary illustration and not for purposes of limitation, it will beunderstood by those skilled in the art that various changes in form anddetail may be made therein without departing from the spirit and scopeof the invention.

What is claimed is:
 1. A distributed series reactor module adapted foroperation over a range of high voltages by having: a) a single virtualground connection to the powerline it is serving in order to establish acommon reference voltage within the support electronics; b) a conductivecase connected to the virtual ground; c) and control communications thatuse a wireless communications link.
 2. The distributed series reactormodule of claim 1 where the virtual ground connection is made to aterminal of the series reactor module, or to a point electricallyequivalent to the powerline potential.
 3. The distributed series reactormodule of claim 1 that utilizes the transmission line per se as a singleturn primary for a reactance transformer.
 4. The distributed seriesreactor module of claim 1 that utilizes a multiple-turn primary for areactance transformer.
 5. A distributed series reactor module adaptedfor operation over a range of high voltages by having: a) a singlevirtual ground connection to the powerline it is serving in order toestablish a common reference voltage within the support electronics; b)a conductive case connected to the virtual ground; c) controlcommunications that use a wireless communications link; d) one or morecorona rings conductively connected to the conductive case.
 6. Thedistributed series reactor module of claim 5 where the virtual groundconnection is made to a terminal of the series reactor module, or to apoint electrically equivalent to the powerline potential.
 7. Thedistributed series reactor module of claim 5 that utilizes thetransmission line per se as a single turn primary for a reactancetransformer.
 8. The distributed series reactor module of claim 5 thatutilizes a multiple-turn primary for a reactance transformer.
 9. Adistributed series reactor module adapted for operation over a range ofhigh voltages by having: a) a virtual ground defined by a connection tothe power transmission line at one terminal of the series reactormodule; b) a conductive case connected to the virtual ground; c) one ormore corona rings conductively connected to the conductive cases; andwhere a reactance is defined by a multiturn coil magnetically coupled toa ferromagnetic core of a reactance transformer.
 10. An active impedanceinjection module adapted for operation over a range of high voltages byhaving: a) a single virtual ground connection to the powerline it isserving in order to establish a common reference voltage within thesupport electronics; b) a conductive case connected to the virtualground; c) and control communications that use a wireless communicationslink.
 11. The active impedance injection module of claim 10 where thevirtual ground connection is made to a terminal of the active impedanceinjection module, or to a point electrically equivalent to the powerlinepotential.
 12. An active impedance injection module adapted foroperation over a range of high voltages by having the followingfeatures: a) a single virtual ground connection to the powerline it isserving in order to establish a common reference voltage for activeimpedance injection module support electronics; b) a conductive caseconnected to the virtual ground; c) control communications that use awireless communications link; d) one or more corona rings conductivelyconnected to the conductive case.
 13. The active impedance injectionmodule of claim 12 where the virtual ground connection is made to aterminal of the active impedance injection module, or to a pointelectrically equivalent to the powerline potential.